﻿<p>An <em>IfcSurface</em> is a 2-dimensional representation item positioned in 3-dimensional space. 2-dimensional means that each point at the surface can be defined by a 2-dimensional coordinate system, usually by u and v coordinates.</p>

<blockquote class="extDef">
NOTE&nbsp; Definition according to ISO/CD 10303-42:1992<br>
A surface can be envisioned as a set of connected points in 3-dimensional space which is always locally 2-dimensional, but need not be a manifold.<br>
Each surface has a parametric representation of the form</blockquote>
<blockquote><img src="../../../figures/ifcsurface-math1.png" width="60" height="24"></blockquote>
<blockquote class="extDef">where u and v are independent dimensionless parameters. The unit normal N, at any point on the surface, is given by the equation</blockquote>
<blockquote><img src="../../../figures/ifcsurface-math2.png" width="236" height="25"></blockquote>

<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>surface</strong> defined in ISO
10303-42.</blockquote>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC1.5
</blockquote>
 
<p class="spec-head">Informal Propositions:</p> 
<ol> 
<li>A surface has non zero area.</li> 
<li>A surface is arcwise connected.</li> 
</ol> 